ESA’s Euclid telescope provides remarkable insights into formation of galaxies and supermassive black holes
Why do galaxies look so different from one another? From beautiful blue spirals like our Milky Way to golden ellipticals like the Messier 87? ESA’s Euclid space telescope is beginning to answer this question within just one year of observation, offering new insights into how galaxies form, grow, and transform over time.
One of Euclid’s main missions is to study what shapes the universe’s galactic population. With its sharp observation and wide-field view, Euclid has already found more than 1.2 million large galaxies and obtained details of their morphology—the shapes, sizes, colors, and masses that reveal their story, as per the Euclid Consortium. Data from Euclid is helping scientists at the Max Planck Institute for Extraterrestrial Physics (MPE) to study how galaxies merge and host supermassive black holes.
According to researchers at Max Planck Institute for Extraterrestrial Physics (MPE), the data from Euclid indicate that galaxies begin their lives as blue, star-forming discs, as shown on the right side of the Hubble diagram given above. Over time, they burn through their gas, collide and merge, gradually transforming into larger elliptical systems. Euclid’s observations not just show the present but also how they got here. “Euclid offers an unprecedented combination of sharpness and sky coverage, it will map the entire extragalactic sky,” says Maximilian Fabricius, scientist at MPE, which built major parts of the telescope’s optics. “For the first time, we can systematically study how the shapes and central structures of galaxies relate to their formation history on truly cosmic scales.”
With their team, Fabricius and Roberto Saglia have already identified hundreds of galaxies with secondary nuclei that may eventually create supermassive black hole binaries. “The most massive black holes lie at the centres of giant elliptical galaxies and are thought to grow primarily through mergers with other supermassive black holes,” added Fabricius. “By detecting and analysing secondary nuclei, Euclid enables us to explore how these enormous black holes continue to grow and how their growth influences the galaxies that host them.”
Euclid’s Q1 release spans 63 square degrees of the extragalactic sky, barely 0.5 % of what the whole target is. But this data is already enough to accelerate discoveries and studies across multiple fields of extragalactic astronomy. Among them is a study led by Daniela Vergani and co-led by Christoph Saulder (MPE), which uncovered 65 galaxies with highly ionized emission lines. Such features are indicative of extreme astrophysical phenomena like active galactic nuclei, shock fronts, or Wolf–Rayet stars, each providing insight into feedback mechanisms responsible for shaping galaxy evolution.
Thanks to Euclid, it is now also evident that the universe is mostly populated by dwarf galaxies, instead of huge spirals. So far, 2,674 dwarfs have been spotted, about 58 % dwarf ellipticals and 42 % dwarf irregulars, per the Euclid Consortium. Many of these galaxies show compact blue cores or globular clusters. These small systems are thought to be the foundation of larger galaxies, offering insights into how systems like the Milky Way came to be.
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